HR 8844: a new transition object between the Am stars and the HgMn stars ?

Abstract

While monitoring a sample of apparently slowly rotating superficially normal early A stars, we have discovered that HR 8844 (A0 V), is actually a new Chemically Peculiar star. We have first compared the high resolution spectrum of HR 8844 to that of four slow rotators near A0V ($\nu$ Cap, $\nu$ Cnc , Sirius A and HD 72660) to highlight similarities and differences. The lines of Ti II, Cr II, Sr II and Ba II are conspicuous features in the high resolution high signal-to-noise SOPHIE spectra of HR 8844 and much stronger than in the spectra of the normal star $\nu$ Cap. The Hg II line at 3983.93 Å is also present in a 3.5 \% blend. Selected unblended lines of 31 chemical elements from He up to Hg have been synthesized using model atmospheres computed with ATLAS9 and the spectrum synthesis code SYNSPEC48 including hyperfine structure of various isotopes when relevant. These synthetic spectra have been adjusted to the mean SOPHIE spectrum of HR 8844, and high resolution spectra of the comparison stars. Chisquares were minimized in order to derive abundances or upper limits to the abundances of these elements for HR 8844 and the comparison stars. HR 8844 is found to have underabundances of He, C, O, Mg, Ca and Sc, mild enhancements of Ti, V, Cr, Mn and distinct enhancements of the heavy elements Sr, Y, Zr, Ba, La, Pr, Sm, Eu and Hg, the overabundances increasing steadily with atomic number. This chemical pattern suggests that HR 8844 may actually be a new transition object between the coolest HgMn stars and the Am stars.

50 pages, 9 figures, accepted in the Astrophysical Journal. arXiv admin note: text overlap with arXiv:1602.04437

References in corpus (10)

• A Catalog of Multiplicity among Bright Stellar Systems
• Improved Laboratory Transition Probabilities for Ce II, Application to the Cerium Abundances of the Sun and Five r-process Rich, Metal-Poor Stars, and Rare Earth Lab Data
• Improved Laboratory Transition Probabilities for Er II and Applications to the Erbium Abundances of the Sun and Five r-Process Rich, Metal-Poor Stars
• Rare-earth elements in the atmosphere of the magnetic chemically peculiar star HD 144897. New classification of the Nd III spectrum
• Improved V II log($gf$) Values, Hyperfine Structure Constants, and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937
• A new method for the inversion of atmospheric parameters of A/Am stars
• A study of the elements copper through uranium in Sirius A: Contributions from STIS and ground-based spectra
• Four new HgMn stars: HD 18104, HD 30085, HD 32867, HD 53588
• The nature of the late B-type stars HD 67044 and HD 42035
• Ultraviolet Spectral Synthesis of Iota Herculis

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• The surface composition of six newly discovered chemically peculiar stars. Comparison to the HgMn stars $\mu$ Lep and $\beta$ Scl and the superficially normal B star $\nu$ Cap
• Chemically Peculiar Stars in the Open Cluster Stock 2